[time-nuts] Building a GPSDO & trouble using Jupiter-T

Ray Xu rayxu123 at gmail.com
Sun Jan 29 22:22:00 EST 2012

Hi Erno

Thanks for your suggestion; while it is convenient to have everything
already planned out, I'm inclined on DIY'ing as much as I can :-)

Ray Xu

On Sun, Jan 29, 2012 at 1:01 AM, Erno Peres <ernieperes at aol.com> wrote:

> Hi Ray,
> please find on this link the info what you are looking for.
>         http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm
> Rgds Ernie.
> -----Original Message-----
> From: Ray Xu <rayxu123 at gmail.com>
> To: time-nuts <time-nuts at febo.com>
> Sent: Sun, Jan 29, 2012 7:51 am
> Subject: [time-nuts] Building a GPSDO & trouble using Jupiter-T
> Hi guys
> I'm planning to build a GPSDO to use as a frequency ref for my GHz
> ventures.
> I've done research in what other people have built - but I have no
> xperience working with long-term precision/stability products (nor do I
> ave the equipment to do so -- I think).
> I'm using the Jupiter T (the one with the 10-pin header) GPS and its 10KHz
> utput in an analog PLL that controls a 10MHz VCXO.  It would be ideal for
> e that if I were to multiply the 10MHz output up to 10GHz, I would get
> bout a few Hertz or so of inaccuracy.  It would also be ideal if I can
> ave a PLL lock time of a few minutes while maintaining accuracy.
> However, right now as I am trying to design my project, I can't find enough
> nformation on the web regarding the VCXO's (or the PLL oscillator, in this
> ase) short term accuracy effect on output frequency.  I know that its
> hort term accuracy depends on the "response time" of the PLL, which also
> epends on the amount of jitter from the Jupiter-T's 10KHz output...  I
> now that the longer the time constant for the PLL, the better accuracy,
> ut I do not want to wait, literally, hours for it to lock...
> Also, what is the advantage of using a OCXO instead of a VCXO in terms of
> hort-term accuracy?  If the PLL time constant is only a few seconds, then
>  crystal shouldn't deviate in frequency by too much within a few seconds,
> ssuming I'm using a crystal bought from a well-known manufacturer...or
> ould it? I am inclined towards using oscillators that do not require any
> ignificant warm up time...
> For those who have experience using the Jupiter T GPS:
>  have bought this
> ttp://
> www.ebay.com/itm/Navman-jupiter-T-Tu60-GPS-Kit-1pps-10khz-GPS-Module-/260790984470but
>  could not get it to communicate via serial.  So far, I do not have
> n
> ntenna available and so the antenna port is just left disconnected.  When
>  turn it on, there is a 1pps and 10KHz signal and the TX line is at logic
> igh.  However, I cannot get it to communicate to anything else, even a
> umb terminal.  It does not respond to when I send a message ID to it.
> Because of computer difficulties, I am using the PicKit 2's UART tool).
> s my device a dud or am I doing something wrong?
> Many inputs is highly appreciated.  Thanks
> --
> _________
> 3, Ray Xu
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73, Ray Xu

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